1. Field of the Invention
This invention pertains to focal plane shutters having two single blades and the guiding, driving, stopping, and rewinding structures and mechanisms therefor, as well as the supporting camera body structure.
2. Discussion of the Prior Art
Apart from the prior art pertaining to focal plane shutters of the kind having oppositely moving blades and the kind having blades which move in a straight line and in the same direction to make an exposure, two groups of patents are of specific interest. The first group pertain to stopping high speed shutter mechanisms, and the second group have to do mostly with the shutter blades themselves.
My U.S. Pat. No. 2,691,331 Oct. 1954, and a division thereof, U.S. Pat. No. 2,803,181 Aug. 1957, pertain to an interlens shutter having two sets of blades and in which the primary shutter driving structures are each brought to a smooth stop by a driven cam and a sliding follower unitary structure which includes a second sliding follower which coacts with the back of the driven cam during rewind thereof to effect follower reset. The energy is dissipated in sliding friction against a spring loaded brake member.
German Pat. No. 561,859 to Zeiss, Oct. 1932, and U.S. Pat. No. 3,511,158, to Nerwin, May 1970, both show shutter curtains of the metal jalousie type which are stored in semi-circular channels partially surrounding the film spools. The curtains are driven by geared sprockets which engage the jalousie bars of the curtains. Jalousie curtains are generally heavy and expensive to manufacture, as well as being somewhat noisy.
Another invention in this second group is U.S. Pat. No. 3,646,603 to Ort et al, Feb. 1972, is simplified over the Zeiss and Nerwin patents in having each curtain made of a single piece of thin metal, which are stored in reverse curved channels. These blades have required transverse stiffening corrugations along the bendable length of each blade as well as stiffening bars at both ends of each blade. The required transverse corrugations are undesirable for blades which must operate at high curtain velocities, i.e., over two hundred inches a second. This is particularly so with the closing blade which is pushed around the curves in the guide channels as well as in the straight channel portion. With very thin metal blades confined in channels this pushing force loads the blade as though it were a column. The transverse corrugations require the guide channels to be sufficiently wide to accommodate the wave height of the corrugations, hence the channels are much too wide for the plain portions of the blades. As a consequence, during the pushing, the blades tend to exhibit columnar buckling and hence bind in the channels during application of the driving force.
It also seems obvious that Ort et al did not comtemplate a high speed shutter because of the inherently flexible blade driving member and its flexible coupling to the driven end of the blade. The driving members have two right angle bends and a necked down portion at the first bend from the drive shaft. Hence the application of any force sufficient to drive the blade at high speed would cause bending of the member and thus a spring coupling dissipating part of the driving force.
Prior to the issuance of my U.S. Pat. No. 2,691,331 a production version of that shutter was produced which had a three and one-half inch aperture. In this large version, which had a shortest total time of one three-hundredth of a second and hence extremely high driving forces, the sliding cam-followers of the patent were replaced by a rocking cam pair at each driving member. These rocking cam pairs, which rolled against each other, were circularly configured and operated through a much larger angle than the present invention. Kinetic energy transferred to each follower cam was dissipated by friction. Each follower cam had a lever portion with a pivoted brake shoe at the end thereof which slid along an arcuate friction surface of a large brake member which, in turn, was located by two limit stops and spring loaded into positive engagement. During braking, there was essentially no winding of the loading spring as is done in this invention. The limit stops and loading spring held the arcuate surface of the brake member at essentially a fixed radius from the axis of the follower cam pivot. The spring biased pivoted brake shoe released during resetting of the follower cam. Each follower cam was reset by a sliding cam and lever arrangement. The use of rocking cams for resetting was not considered. Shutters based upon my U.S. Pat. No. 2,691,331 and the divisions thereof were manufactured by Fairchild Camera & Instrument Corp.
The design of rocking cam pairs, also known as rolling cams, which ideally roll against each other without sliding when one cam is driving the other, (coacting), has been well described in the Dec. 11, 1958 issue of Machine Design magazine and in the Sept. 18, 1961 issue of Product Engineering magazine.